Parkinson's disease (PD), the most common movement disorder afflicting millions of Americans, is diagnosed when patients present with cardinal parkinsonian signs, e.g. bradykinesia, rigidity, and tremor, and show favorable response to levodopa (L-DOPA) or dopamine (DA) agonists. However, even at clinical early stage of the disease, PD patients have already lost more than 60-70% of their DA neurons in the nigrostriatal system. Thus, the nature course of this disease makes it very challenging for any neuroprotective medicine to be effective, simply because there are not many neurons to be protected to begin with in PD patients when the diagnosis can be made clinically. While current functional neuroimaging methods with fluorodopa positron-emission tomography (F-Dopa-PET) or beta-CIT single photon emission computer tomography (Beta-CIT-SPECT) show relatively high sensitivity and specificity in assessing nigrostriatal function even before PD patients become symptomatic, they are very expansive, meaning that they are not currently appropriate for routine diagnostic screening. In addition, these methods are not widely accessible, particularly in developing countries, and do not elucidate biological mechanisms of PD progression. We hypothesize that there are unique protein markers for PD, including preclinical PD, in brain tissue, and some of which will be reflected in the human cerebrospinal fluid (CSF). Hence, we are proposing to use a high throughput proteomic approach to identify proteins unique to preclinical PD and PD progression in two models simultaneously, i.e. a nonhuman primate treated with MPTP and familial PD patients secondary to LRRK2 mutations. This is followed by validation of candidate markers in human CSF of in a different but larger set of both sporadic and familial PD patients, including those at preclinical stage as determined by PET imaging. When completed, we anticipate having a panel of makers in CSF that could serve as the basis of a highly sensitive and specific microsphere-based Luminex xMAP assay to diagnose preclinical PD and to monitor PD progression at early stages. This proposal is designated to investigate biomarkers that can detect patients with Parkinson's disease before clinical presentation. This proposal, if successful, can significantly increase the therapeutic window for Parkinson's patients.